G21 National Standard Low Voltage Electrician Exam
Question 1 Which formula is known as Ohm's Law?
A) P = I²R
B) V = IR
C) P = VI
D) R = V² / P
Answer: B
Explanation: Ohm’s Law states that Voltage (V) is equal to Current (I) multiplied by Resistance (R).
Question 2 Which unit measures electrical resistance?
- Ohms (Ω)
- Volts (V)
- Amperes (A)
- Watts (W)
Answer: A
Explanation: Resistance is measured in Ohms (Ω).
Question 3
Kirchhoff’s Current Law states: 1 / 4
G21 National Standard Low Voltage Electrician Exam
- The sum of all voltages in a closed loop is zero
- The sum of currents entering a node equals the sum leaving it
- Current is the derivative of voltage in time
- Power is the product of current and voltage
Answer: B
Explanation: Kirchhoff’s Current Law (KCL) says the algebraic sum of currents at a node is zero (incoming = outgoing).
Question 4
Kirchhoff’s Voltage Law can be summarized as:
- The total current in a series circuit is always constant
- The voltage source is equal to the load’s voltage drop
- The sum of voltages around any closed loop is zero
- The power factor is always 1
Answer: C
Explanation: Kirchhoff’s Voltage Law (KVL) states that the sum of voltage rises and drops around a loop is zero.
Question 5 Which equation correctly expresses electrical power?
A) P = I²R 2 / 4
G21 National Standard Low Voltage Electrician Exam
B) P = IR²
C) P = I / R
D) P = R² / I
Answer: A
Explanation: Electrical power (P) can be found by P = I²R, among other forms like P = VI.
Question 6 In a DC circuit, if the voltage is doubled and the resistance remains the same, the current will:
- Stay the same
- Increase twofold
- Decrease by half
- Increase fourfold
Answer: B
Explanation: According to Ohm’s Law (I = V/R), doubling the voltage doubles the current if resistance is constant.
Question 7 What is the symbol for inductance?
- L
- C
C) R 3 / 4
G21 National Standard Low Voltage Electrician Exam
- M
Answer: A
Explanation: Inductance is denoted by the letter L in circuit formulas and schematics.
Question 8
Reactance in an AC circuit is caused by:
- Resistance only
- Inductance or capacitance
- Voltage fluctuations
- Decreasing frequency to zero
Answer: B
Explanation: Reactance is the opposition to AC current due to inductors or capacitors in the circuit.
Question 9 Capacitive reactance (Xc) is inversely proportional to which quantity?
- Capacitance
- Resistance
- Frequency
- Voltage
Answer: C
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